Field of the Invention
The present invention relates to a catalyst layer composition for a fuel cell and an electrode for a fuel cell using the same, a method of preparing an electrode for a fuel cell, a membrane-electrode assembly for a fuel cell, and a fuel cell system using the membrane-electrode assembly.
Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through a chemical reaction of oxidant and hydrogen in a hydrocarbon-based, material such as methanol, ethanol, or a natural gas.
Such a fuel cell is a clean energy source with the potential to replace fossil fuels. A fuel cell includes a stack composed of unit cells, and produces various ranges of power. Since the fuel cell has about four to about ten times higher energy density than a small lithium battery, it has been highlighted as a small portable power source.
Typical examples of fuel cells are polymer electrolyte membrane fuel cells (PEMFC) and direct oxidation fuel cells (DOFC). A direct oxidation fuel cell that uses methanol as a fuel is called a direct methanol fuel cell (DMFC).
A polymer electrolyte membrane fuel cell (PEMFC) has an advantage of high energy density and high power, but it has problems in the need to carefully handle hydrogen gas and the requirement of accessory facilities, such as a fuel reforming processor for reforming methane, methanol, natural gas, and the like, in order to produce hydrogen as the fuel gas.
On the contrary, a direct oxidation fuel cell (DOFC) has lower energy density than that of the polymer electrolyte membrane fuel cell, but the direct oxidation fuel cell has advantages of easy handling of a fuel, being capable of operating at room temperature due to its low operation temperature, and the direct oxidation fuel cell does not need additional fuel reforming processors.
In the above-mentioned fuel cell system, the stack that generates electricity substantially includes several scores of unit cells stacked adjacent to one another, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly (MEA) is composed of an anode (also referred to as a “fuel electrode” or an “oxidation electrode”) and a cathode (also referred to as an “air electrode” or a “reduction electrode”) those are separated by a polymer electrolyte membrane.
A fuel is supplied to an anode and adsorbed on catalysts of the anode, and the fuel is oxidized to produce protons and electrons. The electrons are transferred into a cathode via an external circuit, and the protons are transferred into the cathode through the polymer electrolyte membrane. In addition, an oxidant is supplied to the cathode, and then the oxidant, protons, and electrons are reacted on catalysts of the cathode to produce electricity along with water.